Evap coil cleaning (CD5AXA060024ABAA)

Hello. I'm looking for some advice on my system and coil cleaning. I have a carrier infinity system with coil model CD5AXA060024ABAA. When I bought the house two years ago, I noticed that the electronic air cleaner was switched off. The EAC prefilter was really dirty. I just removed the EAC elements and replaced with a 4" media filter because EACs are too much work to clean in my opinion. Then I noticed the A-coil was freezing over. I tired to clean the coil and called a technician out for repair. He told me two things: (1) compressor was not original carrier and looked like it had been replaced; (2) the txv was an r-22 model and he replaced it with an r-410a model. He suspected that the compressor had probably been replaced due to the incorrect expansion valve. When he worked on the system to replace the txv (located just outside the evap coil enclosure), he couldn't get the all the refrigerant back into the condenser, so he had to add some (after replacing the valve of course). Presumably the refrigerant charge was correct at that time.

Last year, I replaced the filter media. AC was functioning normally. In the winter, I noticed that the furnace high limit trips (according to the service mode event history on the infinity thermostat) if the return closest to the unit is blocked (toy box tends to move in front of it).

This year, the evap coil is freezing again. It seems to ice up across the center on the front and most of the surface on the back. I have this feeling that the underside of the coil is really dirty because the system could have been running for years without an effective filter. The blower wheel was/is dirty too (tried to clean that with vacuum two years ago). When I open the evap access panel, I don't have access to the end caps of the coil. In other words, I am looking at the fins on one side. My cleaning technique has consisted of spraying coil cleaner on the front and reaching over the top of the coil and spraying on the back as best I can.

Here are my questions. If I remove more of the duct/evap casing so I have access to the end cap, will I be able to remove the end cap to clean the underside of the a-coil? How else can this be done without pulling the coil? Is cleaning from the top side likely to be enough? I have an appt on wed. with another technician but would like to get some opinions on whether it would be worth pulling the coil to clean it. Thanks for reading!

If you can rig up a manometer and measure the pressure difference between the return & supply sides of the air handler, clean the parts you can easily access, then re-measure you can see if it made a significant difference. Use your best vacuum cleaner with the highest suction and a smaller detailing brush type tip to see if you can't really clear anything that has gotten between the fins. I you have any bent/flattened fins on the coil use a purpose-made coil-comb to gently open them back up.

But if it looks like this on the other side, you may be better off replacing it, since the condensation soaked into the crud will often have corroded the fins to the point of reducing their heat transfer rate:

I was able to use my usb camera to get a picture on the inside of the coil and the blower wheel. The coil doesn't look too bad but difficult to tell how much dirt is caked in the fins. I am thinking about removing the blower assembly to clean it and using a garden hose to flush the evap better. Would having water flow down around the heat exchanger cause problems?

Since it's designed to condense moisture from the air (latent cooling), occasional wetting won't damage it. High-pressure water sprays might bend the fins, but you'd be able to gauge that.

Your picture looks pretty clean- is that frost on the coil? If yes, let the thing idle for a half-hour or so, and shoot it again with the frost gone to verify how much is frost vs. built-up dirt/crud. With that much light coming through I doubt it really needs to be cleaned- you're probably getting sufficient air flow, so you're back to refrigerant charge/volume issues as the proximate cause of the frost-up.

No frost because it has been switched off for a couple of days now and fully defrosted. The light is not coming through the coil--it is just a reflection off the tubing/fins. The camera has an LED light on the end of it and I could hardly see any light coming through from inside to out.